This invention relates to a chemically amplified resist composition which can be effectively used for micro-processing a semiconductor element using various types of radiation such as KrF or ArF excimer laser as far ultraviolet rays, X-ray as synchrotron radiation and electron beam as charged particle radiation and more particularly, to the chemically amplified resist composition comprising A) a polymer containing acid-decomposable functional groups for the manufacture of a resist, B) an acid generator, and C) a low molecular additive which can serve to enhance the dry etch resistance and resolution of patterns.
In general, a semiconductor element is prepared through a lithographic process, wherein a resist is implanted on a silicon wafer to form a film; the film is radiated by a light to form a pattern, followed by development to form a positive or negative pattern.
In parallel with the recent trend that the semiconductor technology is being developed in a higher integration, higher density, smaller size and higher speed due to LSI and VLSI, there has been great demand for the micro-processing of the semiconductor element having ultramicro-patterns of less than 0.2 micron. To meet such market need, a wavelength in the exposed regions has been far shorter from the conventional g-ray or i-line and thus, a new lithography technology using far ultraviolet rays, KrF or ArF excimer laser, X-ray and electron beam have drawn keen attention.
In the case of an ultraviolet ray such as i-line that has been mainly used in the conventional lithographic process, its micro-processing at the subquarter(0.25) micron level is reported to be extremely difficult. Therefore, to achieve the micro-processing at the subquarter micron level, an excimer laser with more short wavelength at the far ultraviolet rays can be utilized, together with X-ray and electron beam; among them, KrF or ArF excimer laser is being spotlighted from the related field.
A resist (hereinafter referred to as xe2x80x9cchemically amplified resistxe2x80x9d) composition suitable for such excimer laser comprises a component having functional groups acid-decomposable (polymer), a component generating by irradiation (hereinafter referred to as xe2x80x9cacid generatorxe2x80x9d) and a solvent, which is being applied in the lithographic process using the chemically amplified effect induced by the acid generator.
In line with the chemically amplified resist composition, the Japanese Pat. Heisei 2-27,660 has disclosed a resist composition comprising a polymer with t-butyl ester group of carboxylic acid or t-butylcarbonyl group of phenol, together with an acid generator. This method using the composition is based upon the principle that since t-butyl ester group or t-butylcarbonyl group in a polymer is dissociated and calibrated into hydroxyl group due to the action of acid generated from irradiation, the exposed regions are easily dissolved by an alkaline developer.
However, in the case of the chemically amplified resist used for KrF excimer laser, a phenol resin has been mostly employed as a base material but it has proven to be insuitable for a matrix resin due to the fact that the aromatic ring in the resin absorbs much more light from ArF excimer laser. To comply with this matter, intensive research for polyacrylate derivatives as a matrix resin has been made, since it has relatively less absorption of light than phenol resin at ArF excimer laser region (Japanese Pat. Heisei 4-226,461 and Proc. SPIE, 1996, vol. 2724, p. 377).
Even though it has less absorption of light at ArF excimer laser region, polyacrylate has a poor dry etch resistance. Recently, to withcome such drawback of polyacrylate, much research has focused on the method of introducing alicyclic derivatives to polyacrylate in order to enhance the etch resistance but the affinity to a developer is decreased due to the fact that such alicyclic derivatives are hydrophobic. Further, to form the pattern of less than 0.2 micron, the adhesion between a resist composition and substrate is an important factor. In the case of the conventional polyacrylate matrix resin, carboxylic acid is introduced to the side chain of polyacrylate in an effort to improve the adhesion (Proc. SPIE, 1997, vol. 3049, p. 126). However, if the amount of carboxylic acid is increased to some extent, the increasing solubility to a basic solution makes it inevitable to change the basic concentration of a developer.
The matrix resin with hydrophilic groups, which can serve to improve a dry etch resistance, include a copolymer of maleic anhydride and olefin (Proc. SPIE, 1997, vol. 3049, p. 92). With its hydrophilic property, maleic anhydride can serve to facilitate the co-polymerization with an olefin-based monomer at a very low temperature and pressure. The olefin-based monomer can promote a dry etch resistance and resolution through the introduction of various substituents at the side chain of the copolymer (Proc. SPIE, 1998, vol. 3333, p. 463). Further, to overcome the shortcomings that the copolymer resin using maleic anhydride and olefin-based monomer has encountered (e.g., reduction of remaining film characteristics, decrease of dry etch resistance or occurrence of standing wave (?) in forming the patterns), the recent method of using a low molecular additive for the manufacture of a resist has been greatly spotlighted (Korea Pat. No. 98-064842 and Proc. SPIE, 1998, vol. 3333, p. 73).
An object of this invention is to provide a chemically amplified resist composition, which is activated by far ultraviolet rays represented by KrF or ArF excimer laser as a chemically amplified resist, and with its excellent transparency on ArF excimer laser beam, the composition has excellent combination of properties such as resolution and sensitivity, including substrate adhesion, dry etch resistance and development properties.
To achieve the above object, the chemically amplified resist composition of this invention is characterized by the chemical composition containing a multi copolymer copolymer represented by the following formula 1, a low molecular additive represented by the following formulae 2 or 3, an acid generator and a solvent. 
wherein the repeating units comprising X and Y are independent monomers, respectively, selected from the group consisting of the following formulae (II), (III) and (IV); 
wherein R1 is a hydrogen atom, a linear or branched alkyl group, a cyclic or polycyclic alkyl group, an alkyl carbonyl group, a branched alkyl carbonyl group, a cyclic or polycyclic alkyl carbonyl group of 1 to 20 carbon atoms such as an acetyl group, a t-butyl oxycarbonyl group, a cyclohexane carbonyl group, an adamantane carbonyl group a bicyclo[2,2,1]heptane methyl carbonyl group.
R2 is a hydrogen atom, a hydroxyl group, carboxylic group, an alkyl group, an alkyl group containing an alkoxy group, a hydroxyl group or a carboxylic acid, an alkoxy group, a linear alkyl oxycarbonyl group, a branched alkyl oxycarbonyl group, an alkoxy alkyl carbonyl group, a cyclic alkyl oxycarbonyl group or polycyclic alkyl oxycarbonyl group of 1 to 20 carbon atoms.
R3 is a hydrogen atom, a linear or branched alkyl group, a cyclic or polycyclic alkyl group of 1 to 20 carbon atoms such as a methyl group, an ethyl group, a t-butyl group, an isopropyl group, an adamantyl group, a bicyclo[2,2,1]heptane methyl group.
l, m, n and o, which represent the repeating units of a polymer, are 0xe2x89xa6l/(l+m+n+o)xe2x89xa60.5, 0xe2x89xa6m/(l+m+n+o)xe2x89xa60.5, 0xe2x89xa6n/(l+m+n+o)xe2x89xa60.35 and 0.4xe2x89xa6o/(l+m+n+o)xe2x89xa60.6, respectively, with a value of 0.15xe2x89xa6(1+m)/(l+m+n+o)xe2x89xa60.5. 
wherein R1 is the same as defined above. 
wherein R2, R3 is the same as defined above.
To further improve various shortcomings of the conventional chemically amplified positive resist in terms of a substrate adhesion, dry etch resistance and development, the inventor et al. have endeavored to improve the dry etch resistance with the introduction of a cyclic structure comprising maleic anhydride and norbornene derivatives to the main chain, while enhancing the adhesion with a substrate via introduction of hydroxyl group at the side chain of repeating units. In addition to that, further improvement of sensitivity and resolution during the manufacturing process of resist is ensured by introducing other different acid-decomposable functional groups. In particular, through a new introduction of a low molecular additive containing some functional groups which serve to inhibit the dissolution in the non-exposed regions but is acid-decomposable, the inventor et al have intended to improve the vertical at the side wall of pattern as well as resolution.
(A) Polymer
The polymer used for this invention comprises a repeating units consisting of maleic anhydride, norbornene or norbornene carboxylic acid derivatives, anhydrous norbornene carboxylic acid derivatives and norbornene derivatives whose side chains contain hydroxyl group or acid-decomposable functional group. Further, the polymer itself, so obtained from this invention, is insoluble or less soluble to alkaline solution with one or more of the protecting groups dissociated by an acid generator.
The alkali solubility of a polymer can be adjusted depending on the contents of acidic functional groups decomposed by an acid generator. As such, a variety of polymers can be prepared by selecting from norbornene derivatives and adjusting their contents in the main chain. The resist containing such polymer can have excellent combination of properties such as a dry etch resistance and substrate adhesion. On top of that, a resist composition with better sensitivity, resolution and thermal resistance can be obtained. The polymer used for this invention is a multi copolymer copolymer whose repeating units is represented by the formula 1.
Since each structure of the monomers, which are represented by the formulae (II), (III) and (IV), has hydroxyl group, carboxylic acid or one or more of acid-decomposable functional groups, including a linear or cyclic hydrophobic group, a resist containing such polymer of these monomers may serve to enhance the inhibitory effect of dissolution in the non-exposed regions, while enhancing the dry etch resistance.
The monomer, which is represented by the formula (II), is 3-bicyclo[2,2,1]hept-5-ene-2-yl-3-hydroxyl-propionic acid t-butyl ester (hereinafter referred to as xe2x80x9cBHPxe2x80x9d) or other compounds derived from BHP. The detailed examples are as follows: 
The monomer, which is represented by the formula (III), is norbornene carboxylic acid or other compounds derived from norbornene carboxylic acid. The detailed examples are as follows: 
The monomer, which is represented by the formula (IV), is anhydrous norbornene carboxylic acid or other compounds derived from anhydrous norbornene carboxylic acid. The detailed examples are as follows: 
The polymer, which is represented by the formula 1, can be obtained via multi copolymer co-polymerization among norbornene, maleic anhydride and a monomer selected from norbornene derivatives represented by the formulae (II)xcx9c(IV). It is preferred that when the norbornene derivatives represented by X and Y are selected, X is selected from some norbornene derivatives containing hydroxyl group or carboxylic acid (e.g.: norbornene derivatives represented by the formulae (II-9), (III-3) and (IV-1), while Y is selected from norbornene derivatives which contain no hydroxyl group or carboxylic acid but with acid-decomposable functional groups.
The examples of multi copolymer copolymers, so polymerized by the above-mentioned method include the following polymers. The contents of repeating units contained in each resin can be appropriately adjusted in consideration of sensitivity, substrate adhesion and resolution. 
wherein R1, R2, R3, l, m, n and o are the same as defined above.
The multi copolymer copolymer may be a block copolymer, a random copolymer or graft copolymer. According to this invention, the preferred multi copolymer copolymer is an alternative copolymer between maleic anhydride and norbornene derivatives or a random copolymer.
The polymerization process represented by the formula 1 may be conducted via a commonly available method but a solution polymerization is preferable using a radical polymerization initiator. The examples of the radical polymerization initiator include azo compounds selected from the group consisting of azobisisobutyronitrile (AIBN), dimethyl 2,2xe2x80x2-azobisisobutyrate, 1,1xe2x80x2-azobis(cyclohexane-1-carbonitrile), 2,2xe2x80x2-azobis(2-methylbutyronitrile), 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), azobisisocapronitrile, azobisisovaleronitrile; or benzoyl peroxide (BPO); lauryl peroxide; and t-butylhydroperoxide. There is no special restriction for use if general types of radical polymerization initiators are employed.
The polymerization may be conducted via bulk polymerization, solution polymerization, suspension polymerization, bulk-suspension polymerization and emulsion polymerization; the examples of solvents during the solution polymerization include one or more of the solvents selected from the group consisting of benzene, toluene, xylene, benzene halide, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetates, esters, lactones, ketones and amides.
The polymerization temperature of polymers represented by the formula 1 can be appropriately selected depending on the types of polymerization initiator. For example, when, a polymerization initiator is azobisisobutyronitrile, its appropriate temperature is in the range of 60xcx9c80xc2x0 C.
The molecular weight and molecular weight distribution of polymer may be appropriately adjusted depending on the amount of polymerization initiator and reaction time. After the polymerization is completed, it is preferred that the remaining monomer in a reaction mixture and by-products are removed by a solvent-precipitation method. The solvent used for precipitation may vary depending on the types of polymerization solvent and the structure of monomers used therein. In general, the examples of useful polymerization solvent include methanol, a co-solvent containing methanol and distilled water, ethanol, isopropyl alcohol, a co-solvent containing isopropyl alcohol and hexane, hexane and ether.
The polystyrene-calibrated weight average molecular weight (hereinafter referred to as xe2x80x9cMwxe2x80x9d) of the polymer, which is represented by the formula 1, is commonly in the range of 1,000xcx9c100,000 by gel permeating chromatography (GPC); the preferred Mw of polymer is in the range of 3,000xcx9c50,000 in terms of sensitivity, development, coating property and thermal resistance as a photoresist.
If the Mw of polymer is less than 1,000, the coating and development properties will be significantly reduced due to poor formation of film, when the resist composition of this invention is applied to a substrate; in case of exceeding 100,000, various properties of the resist composition in terms of sensitivity, resolution and development will be reduced. The distribution of molecular weight of polymer is preferably in the range of 1.0xcx9c5.0, more preferably in the range of 1.0xcx9c3.0.
To measure the molecular weight and molecular weight distribution on polymers, so synthesized, GPC analysis instruments is used 1100 series device (HP Co.) and TriSEC detector (Viscotek Co.) under the following analytical conditions:
Column: G2500HXL (1 e.a.) and G4000HXL (1 e.a.)
Eluent: tetrahydrofuran
Flow rate: 1.0 ml/min.
Column temperature: 40xc2x0 C. using a monodispersion polystyrene as standard. According to this invention, one or more of the polymer used for a resist may be used.
(B) Photoacid Generator
The acid generator used for the resist composition of this invention include iodonium salt, sulfonium salt, phosphonium salt, diazonium salt, pyridinium salt as an onium salt series; among them, the examples of the preferred salts include triphenylsulfonium triflate, diphenyl(4-methylphenyl)sulfonium triflate, diphenyl(4-t-butylphenyl)sulfonium triflate, diphenyl(4-methoxyphenyl)sulfonium triflate, diphenyl(naphtyl)sulfonium triflate, dialkyl(naphtyl)sulfonium triflate, triphenylsulfonium nonaflate, diphenyl(4-methylphenyl)sulfonium nonaflate, diphenyl(4-butylphenyl)sulfonium nonaflate, diphenyl(4-methoxyphenyl)sulfonium nonaflate, diphenyl(naphtyl)sulfonium nonaflate, dialkyl(naphtyl)sulfonium nonaflate, tridiphenylsulfonium hexafluoroantimonate, diphenyliodonium triflate, diphenyliodonium methylbenzene sulfonate, bis(cyclohexylsulfonyl)diazomethane and bis(2,4-dimethylphenylsulfonyl)diazomethane.
Unlike the conventional acid generator, the onium salt represented by the following formula 4 serves to inhibit the dissolution in the unexposed regions, while promoting the dissolution in the exposed regions. Formula 4 
wherein R4 and R5 are independently a linear or branched alkyl group, a cyclic or polycyclic alkyl group, or an aryl group;
R6 and R7 are independently a hydrogen atom, an alkyl group, or an alkoxy group;
p is an integer of 0xcx9c14.
The amount of the acid generator is contained in the range of 0.1xcx9c30 weight parts on the basis of 100 weight parts of the polymer, preferably in the range of 0.3xcx9c10 weight parts. According to this invention, one or more of the acid generators can be employed.
(C) Low Molecular Additive
The low molecular additive used for this invention can serve to improve a dry etch resistance through the introduction of cyclic structure within the molecules, while improving the vertical of the side walls of resist patterns with better contrast in development by enhancing the remaining film characteristics in the unexposed regions and by facilitating the dissolution on alkaline developer induced by acid in the exposed regions.
The compounds, which can serve to promote the dissolution rate of a developer through their decomposition by acid, include alicyclic derivatives that can be easily calibtated into deprotecting groups by acid.
The low molecular additives used for this invention is the compound represented by the formula 2 or 3, which belongs to norbornane-based compound where the double bond of norbornene-based monomer is reduced under hydrogenation.
The examples of the norbornane-based low molecular compound, which is represented by formula 2 or 3, include the following compounds. 
According to this invention, one or more of the low molecular compounds can be employed.
The amount of the low molecular compound used for the manufacture of resist is contained in the range of 3xcx9c50 weight parts on the basis of 100 weight parts of the polymer, preferably in the range of 5xcx9c40 weight parts. If the amount of the low molecular compound is less than 3 weight parts, any effect dose not appear but in case of exceeding 50 weight parts, the adhesion and coating property of resist on a substrate is significantly reduced.
The resist composition of this invention can use some additives, if desired; these additives include a surfactant, a halation inhibitor, an adhesive supplement agent, a storage stabilizer and a defoaming agent.
The examples of the surfactant include polyoxylauryl ether, polyoxystearyl ether, polyoxyethyleneoleyl ether, polyethylene glycol dilaurylate. It is preferred that the amount of the surfactant is containing less than 2 weight parts on the basis of 100 weight parts of the polymer.
Further, to prevent the diffusion of acid generated after exposure, some basic compounds can be employed. It is preferred that the amount of the basic compound is containing in the range of 0.01xcx9c5 weight parts on the basis of 100 weight parts of the polymer. If the amount of the basic compound exceeds 5 weight parts, the diffusion of acid is decreased but the sensitivity of resist becomes poor.
To achieve a homogeneous and flat film of the resist composition according to this invention, some solvents with appropriate evaporation rate and viscosity can be employed.
The examples of such solvent include ethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether, ethyleneglycol monopropyl ether, methylselusolve acetate, ethylselusolve acetate, propyleneglycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, propyleneglycol monopropyl ether acetate, methyl ethyl ketone, cyclohexanone, methyl 2-hydroxylpropionate, ethyl 2-hydroxylpropionate, 2-heptanone, ethyl lactate and gamma-butyrolactone. According to this invention, one or more of the solvents can be employed, if desired.
The amount of solvent is adjusted in such a manner that it can be homogeneously distributed on a wafer through its appropriate use in consideration of volatility, viscosity, etc.
The resist composition of this invention is prepared in the form of solution and then, it is applied to a wafer, followed by a drying process to form a resist film. According to this invention, the coating method is performed in such a manner that the resist solution, so prepared and filtered, may be applied to a wafer substrate by the coating methods of spin, drift or roll.
The resist film coated by the above method, shall be partially radiated to form a micro-pattern. The examples of the radiation include ultraviolet i-line, far ultraviolet KrF excimer laser, ArF excimer laser, X-ray and electron beam as charged particle radiation. There is no special restriction on the types of radiation and the radiation may be selectively used depending on the types of acid generator. After irradiation, the resist film may be heated so as to improve sensitivity thereof.
According to this invention, the developer is selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, ammonia water, ethylamine, n-propylamine, triethylamine, tetramethyl ammonium hydroxide and tetraetylammonium hydroxide; among them, it is preferred to select tetramethyl ammonium hydroxide. Surfactant or water-soluble alcohols may be used as an additive, if desired.